Polymeric films are used in a wide variety of applications. Multilayer polymeric optical films are widely used for various purposes, including as mirrors and polarizers. These films often have extremely high reflectivity, while being lightweight and resistant to breakage. Examples of a wide variety of multilayer films are included in the commonly assigned U.S. Pat. No. 5,882,774, entitled “Optical Film,” which is hereby incorporated by reference. Exemplary applications include compact electronic displays, including liquid crystal displays (LCDs) placed in mobile telephones, personal data assistants, computers, televisions and other devices.
One type of polymer that is useful in creating polarizer or mirror films is a polyester. One example of a polyester-based polarizer includes a stack of polyester layers of differing composition such as described for example in U.S. Pat. No. 6,641,900 (Hebrink et al.). Such stacks are also commonly referred to as a multilayer reflective film. The multilayer reflective films may also include one or more additional layers which, for example, cover at least one surface of the stack of layers to prevent damage to the stack during or after processing.
A polyester is prepared by reactions of one or more different carboxylate monomers (e.g., compounds with two or more carboxylic acid or ester functional groups) with one or more different glycol monomers (e.g., compounds with two or more hydroxy functional groups). One example of a polyester useful in multilayer optical films is polyethylene naphthalate (PEN) which can be made, for example, by reactions of naphthalene dicarboxylic acid with ethylene glycol. The properties of a polyester polymer or film vary with the particular choice of kind and amount of monomer molecules.